Inhibited hydrofluoric acid composition

ABSTRACT

An inhibited hydrofluoric acid aqueous composition, said composition comprising: hydrofluoric acid in solution; and a weak base selected from the group consisting of: lysine, arginine, histidine, glutamine, asparagine, tryptophan, and tyrosine; wherein said weak base and hydrofluoric acid are present in a molar ratio of at least 1:1. Also disclosed is a mud acid using this inhibited acid composition.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Canadian Application No.3,039,288 filed Apr. 5, 2019, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to a novel acid composition for use invarious industries, more specifically it is directed to an inhibitedhydrofluoric acid (HF) and a mud acid using such.

BACKGROUND OF THE INVENTION

Acids have numerous applications across most industries. The use ofacids requires certain safety precautions. All acids are not createdequal, some are mundane and are found in almost every household, e.g.,vinegar. Other acids are highly controlled to avoid major releases,which can cause serious environmental and human exposure consequences.

Hydrofluoric acid, while not a strong acid, i.e., does not dissociatefully in water, is classified as one of the most dangerous substancesused in industry. Even small amounts of dermal exposure can result inorgan failure and death.

Hydrofluoric acid is a solution of hydrogen fluoride (HF) and water. Itis used in the preparation of almost all fluorine compounds, such aspolymers. It is a highly corrosive colourless solution that is capableof dissolving a large number of materials, such as glass (silica) andvarious metals. Because it is highly reactive to glass and corrosive tovarious metals, it must be stored in plastic containment vessels orother non-reactive materials. As a gas (fumes), hydrogen fluoride ispoisonous and can quickly and irreversibly damage soft tissues such aslungs and the corneas of the eyes. Aqueous hydrofluoric acid is acontact-poison with the potential for deep burns that, althoughinitially painless, result in tissue death. By interfering with thebody's calcium metabolism, the concentrated acid may also cause systemictoxicity and eventual cardiac arrest and fatality.

Its widespread use warrants the demand for a safer form of HF to allowhandling, storage and transport thereof without the constant majornegative risks associated with such, and desirably perhaps a looseningof the handling restrictions/requirements.

Prior art, while abundant in its use of HF for various applications,does not provide any indication of an effective, commercially viable,safe alternative for the handling of HF. One can immediately see thevalue of a safer to handle composition of HF given the multipleapplications in multiple industries.

U.S. Pat. No. 8,389,453 teaches a tetrafluoroboric acid and an organicnitrogenous base, related compounds and compositions, can be used inconjunction with various methods of cleaning and/or the treatment ofsubstrate surfaces. It specifically discloses a method for removingsurface contaminants, said method comprising: providing an aqueouscomposition comprising a compound, said compound the acid-base reactionproduct of tetrafluoroboric acid and urea, said urea and saidtetrafluoroboric acid in a molar ratio of about 1.0 to about 3.0, saidurea utilized as a base and dissolved in said composition; andcontacting said composition and a surface comprising at least onecontaminant thereon.

WO2016033259A1 teaches methods for removing and inhibiting deposits,reducing the pH of aqueous mixtures, and increasing recovery of crudeoil from subterranean formations, the methods comprising contacting anacid composition with a liquid that is in contact with a metal surfaceor with a well or formation. The composition comprises a salt of anitrogen base having a fluoro-inorganic anion. In particular, thesemethods are intended for removing deposits and lowering the pH. Thesemethods can be used in steam generators, evaporators, heat exchangers,and the like that use water compositions containing produced water andother water sources in plant unit operations.

U.S. Pat. No. 10,035,949 B2 teaches methods for increasing recovery ofcrude oil from a subterranean hydrocarbon-containing formation and forremoving or inhibiting deposits in a well, the methods comprisingcontacting an acid composition that comprises a salt of a nitrogen basehaving a fluoro inorganic anion with the well or the formation.

Also known is tetrafluoroboric acid with the chemical formula H₃OBF₄. Itis mainly produced as a precursor to fluoroborate salts. It is a strongacid and quite corrosive as it attacks the skin. It is availablecommercially as a solution in water and other solvents such as diethylether. In oil and gas applications it is considered to be a retardedacid which permits deep penetration into the reservoir before the acidis spent, i.e., fully reacted with the formation. For a solution oftetrafluoroboric acid, at no point in time is there a high amount offree HF, making it less reactive than common mud acids. Because of itslong reaction time, tetrafluoroboric acid treatments require longershut-in times compared to common mud acid or HF treatments making themless attractive due to operational restrictions.

In light of the prior art, there remains a need to produce a more HS&Eoriented, technically advanced mud acid system and method of using such.The known uses have undeniable value in various industries but thehealth and environment risks and technically negative aspects associatedwith its use are many and considerable.

SUMMARY OF THE INVENTION

Accordingly, there is a provided a novel composition of inhibited HFwhich allows to overcome certain drawbacks from known HF compositions.

According to an aspect of the present invention, there is provided aninhibited hydrofluoric acid aqueous composition, said compositioncomprising:

-   -   hydrofluoric acid in solution; and    -   a weak base selected from the group consisting of: lysine,        arginine, histidine, glutamine, asparagine, tryptophan, and        tyrosine;        wherein said weak base and hydrofluoric acid are present in a        molar ratio of at least 1:1.

Preferably, there is provided an inhibited hydrofluoric acid aqueouscomposition, said composition comprising:

-   -   hydrofluoric acid in solution; and    -   a weak base selected from the group consisting of: lysine,        arginine, histidine, glutamine, asparagine, tryptophan, and        tyrosine;        wherein said weak base and hydrofluoric acid are present in a        molar ratio of at least 1.1:1.

Preferably, the weak base is lysine.

According to another aspect of the present invention, there is provideda method of preparing an inhibited hydrofluoric acid composition, saidmethod comprising the steps of:

-   -   providing a pre-determined amount of hydrofluoric acid;    -   providing a weak base;    -   adding the amino acid into the hydrofluoric acid until the molar        ratio of weak base:hydrofluoric acid is at least 1.1:1.

According to another aspect of the present invention, there is provideda precursor to an acid composition for use in glass etching, saidprecursor comprising:

-   -   hydrofluoric acid in solution; and    -   a weak base;        wherein said weak base and hydrofluoric acid are present in a        molar ratio of at least 1:1.

According to an aspect of the present invention, there is provided amethod of using a precursor to an acid composition for glass etching,said precursor comprising:

-   -   hydrofluoric acid in solution; and    -   a weak base;        wherein said weak base and hydrofluoric acid are present in a        molar ratio of at least 1:1; and wherein the method comprises        the steps of:    -   providing a glass surface for etching;    -   providing said precursor;    -   exposing said precursor to an acid composition sufficient to        dissociate an amount of HF required to etch glass;    -   applying the precursor-acid composition to said glass surface        for a sufficient time period to etch said glass surface.

Preferably, the acid composition is selected from the group consistingof acids having a pKa value of less than 3. Preferably, the acid havinga pKa value of less than 3 is selected from the group consisting of:hydrochloric acid, nitric acid, sulfuric acid, modified acids, andorganic acids. Preferably, the modified acid is selected from the groupconsisting of: HCl, MEA-HCl, urea-HCl, methanesulfonic acid, sulfuricacid, sulfamic acid, and lysine-HCl. Urea-HCl may come in various molarratios of urea to HCl preferably, ratios below 1:1 are desirable. Ratiosof 0.8:1 and less urea:HCl are more desirable, ratios of 0.7:1 and lessare even more desirable. MEA-HCl may come in various ratios of MEA toHCl preferably, ratios ranging from 1:3 to 1:15 are desirable. Ratiosranging from 1:4 to 1:10 are more desirable. Ratios ranging from 1:5 to1:9 are even more desirable. Lysine-HCl may come in various ratios oflysine to HCl preferably, molar ratios ranging from 1:3 to 1:15 aredesirable. Ratios ranging from 1:4 to 1:10 are more desirable. Ratiosranging from 1:5.5 to 1:9 are even more desirable.

According to an aspect of the present invention, there is provided a mudacid composition comprising:

-   -   an inhibited hydrofluoric acid aqueous composition, said        composition comprising:        -   hydrofluoric acid in solution; and        -   a weak base; and    -   an acid having a pKa value of less than 3;        wherein said weak base and hydrofluoric acid are present in a        molar ratio of at least 1:1. Preferably, the acid with a pKa of        less than 3 is selected from the group consisting of: selected        from the group consisting of: HCl, MEA-HCl, urea-HCl,        methanesulfonic acid, sulfuric acid, sulfamic acid, and        lysine-HCl. Preferably also, said weak base and hydrofluoric        acid are present in a molar ratio of at least 1.1:1.

According to a preferred embodiment of the present invention, the weakbase is selected from the group consisting of: lysine, arginine,histidine, glutamine, asparagine, tryptophan, tyrosine. Preferably, theweak base is lysine.

According to another aspect of the present invention, there is provideda use of an acid composition in the oil industry to perform an activityselected from the group consisting of: stimulating formations; assistingin reducing breakdown pressures during downhole pumping operations;treating wellbore filter cake post drilling operations; treating scaleon cyclical steam, oil sands or SAGD wells or related equipment;assisting in freeing stuck pipe; descaling pipelines and/or productionwells; increasing injectivity of injection wells; lowering the pH of afluid; fracturing wells; performing matrix stimulations; conductingannular and bullhead squeezes & soaks; pickling tubing, pipe and/orcoiled tubing; increasing effective permeability of formations; reducingor removing wellbore damage; cleaning perforations; and solubilizing orstimulating sandstone formations.

According to another aspect of the present invention, there is provideda method of using a mud acid to acidize a sandstone formation, saidmethod comprises the steps of:

-   -   providing an inhibited hydrofluoric acid composition, comprising        a pre-determined amount of hydrofluoric acid; and a        pre-determined amount of a weak base; wherein the molar ratio of        weak base:hydrofluoric acid is at least 1:1;    -   providing an acid composition, said acid composition having a        low pH and adapted to activate the inhibited hydrofluoric acid        composition when put in contact therewith;    -   combining the inhibited hydrofluoric acid composition with said        acid composition to create a mud acid; and    -   applying said mud acid to a silicate-containing formation and        allowing said mud acid composition sufficient exposure time to        dissolve a pre-determined amount of silica.

According to another aspect of the present invention, there is provideda method for removing silica or silicate deposits, said methodcomprising the steps of:

-   -   providing an inhibited hydrofluoric acid composition, comprising        a pre-determined amount of hydrofluoric acid; and a        pre-determined amount of a weak base; wherein the molar ratio of        weak base:hydrofluoric acid is at least 1:1;    -   providing an acid composition, said acid composition having a        low pH and adapted to activate the inhibited hydrofluoric acid        composition when put in contact therewith; and    -   combining the inhibited hydrofluoric acid composition with said        acid composition to create a mud acid.

According to another aspect of the present invention, there is provideda method for removing silica or silicate deposits on a metal surface,said method comprising the steps of:

-   -   providing an inhibited hydrofluoric acid composition, comprising        a pre-determined amount of hydrofluoric acid; and a        pre-determined amount of an weak base; wherein the molar ratio        of weak base:hydrofluoric acid is at least 1:1;    -   providing an acid composition, said acid composition comprising        a corrosion inhibitor package and having a low pH and adapted to        activate the inhibited hydrofluoric acid composition when put in        contact therewith; and    -   combining the inhibited hydrofluoric acid composition with said        acid composition to create a mud acid.

Preferably, said weak base and hydrofluoric acid are present in a molarratio of at least 1.1:1.

Preferably, the corrosion inhibitor package comprises: a metal iodidesuch as potassium iodide; a terpene; optionally, a cinnamaldehyde or aderivative thereof; at least one amphoteric surfactant; a solvent; andoptionally, a non-emulsifier.

Preferably, the addition of the inhibited hydrofluoric acid compositionis done by injecting it directly into the flowing acid composition.According to a preferred embodiment, the addition of the inhibitedhydrofluoric acid composition is done by injecting it directly into theflowing acid composition by a venturi entrainment of the inhibitedhydrofluoric acid by the acid composition.

According to a preferred embodiment of the present invention, the weakbase used in the method is selected from the group consisting of:lysine, arginine, histidine, glutamine, asparagine, tryptophan,tyrosine. Preferably, the weak base is lysine.

DESCRIPTION OF EMBODIMENTS OF THE PRESENT INVENTION Example 1—InhibitedHF Composition

According to a preferred embodiment of the present invention, inhibitedHF can be made by the addition of at least 1 molar equivalent of anamino acid, such as lysine. The subsequent addition of an acid to theinhibited HF composition restores the inhibited HF's ability to dissolvesand, and it has a similar dissolving power when compared to a regularmud acid.

HF was inhibited by the addition of an amino acid such as lysine, untilvery little (i.e. an insignificant amount) quartz (SiO₂) was observed tobe dissolved. A molar ratio of 1:1 weak base to HF or greater was foundto be necessary to inhibit HF's ability to dissolve quartz, and a ratioof 1.1:1 was used during testing to provide a reasonable safety margin.It is assumed that at a ratio of 1.1:1, the hazard for skin contact ofthe solution has largely been eliminated.

Preferably, an inhibited acid should be effective at dissolving metaloxides (especially aluminum oxide) as well as complex silicates. Otherdesirable properties include: the ability to rapidly solubilize ironoxides and ability to dissolve calcium based scales.

Re-Activation of the Inhibited HF Composition

The inhibited HF solution can regain its quartz dissolving potentialthrough the addition of an acidic solution, such as HCl. By themselves,HCl or inhibited HF dissolve essentially no quartz; however, incombination they perform on par with a normal mud acid (HF:HCl).

To evaluate the performance of mud acids created with acid compositionscomprising HCl:MEA in molar ratios of 4.4:1; 6.3:1; and 11.3:1,inhibited HF mud acids were prepared using HCl and acid compositionscomprising HCl:MEA in ratios of 4.4:1; and 11.3:1 with various amount offree HCl (6 to 12%). The results show that mud acids produced with acidcompositions comprising HCl:MEA in ratios of 4.4:1; and 11.3:1 match,and may even exceed, the performance of a standard HCl mud acid.

According to a preferred embodiment of the present invention, the mudacid is first made by preparing an inhibited HF. The inhibited HF can bemade by the addition of at least 1 molar equivalent of a weak basehaving a pKa greater than 7. Compounds which fit these criteria areselected from the group consisting of: lysine, arginine, histidine,glutamine, asparagine, tryptophan, and tyrosine. Preferably, a safetyfactor of 10% is used, so 1.1 molar equivalents of weak base are addedto 1 mole of HF. The subsequent addition of an acid to the inhibited HFcomposition restores the inhibited HF's ability to dissolve sand, and ithas a similar dissolving power to a regular mud acid.

Effects of Mud Acid Compositions Comprising HCl:MEA in Ratios of 4.4:1;6.3:1; and 11.3:1 on Reprecipitation

Three types of reprecipitation products are commonly known to occurduring sandstone acidizing, and are referred to as primary, secondary,and tertiary reaction products.

Primary precipitation products can occur between HF and calcium (fromCaCO₃) to produce calcium fluoride as per equation (1):2HF_((aq))CaCO_(3(s))→CaF_(2(s))+CO_(2(g))+H₂O_((l))  (1)

The precipitation will occur when the concentration of CaF₂ exceeds 0.16g/L. This reaction is avoided by using an acidic pre-flush to clean thenear-wellbore region, and the inhibited HF combined with HCl forexample, will not prevent this reaction if calcium is present.

Secondary precipitation products are those that occur as a result of areaction with hexafluorosilicic acid (H₂SiF₆), which is produced when HFreacts with quartz as shown in equation 2, or with clay (general formulaof Al—Si) as shown in equation 4:6HF(aq)+SiO₂(s)→H₂SiF₆(aq)+2H₂O(l)  (2)(6+x)HF(aq)+Al—Si(s)→H₂SiF₆(aq)+AlF_(x) ^((3-x))+(aq)  (3)

Hexafluorosilicic acid can react with alkali metals (M⁺), typicallysodium or potassium, to produce hexafluorosilicate precipitates as perequation 4:H₂SiF₆(aq)+2M⁺(aq)→M₂SiF₆(s)+2H⁺(aq)  (4)

The precipitation will occur when the concentration exceeds 6.4 g/L forNa₂SiF₆, and 1.8 g/L for K₂SiF₆. Fluid's inhibited mud acid was notexpected to prevent this precipitation, and laboratory trialsdemonstrate that similar amounts of potassium hexafluorosilicate wereprecipitated in comparison to a standard mud acid.

Hexafluorosilicic acid can also react with the aluminum in clays toproduce a silica gel precipitate as shown in equation 5 (unbalanced):H₂SiF₆(aq)+Al³⁺(s)→AlF_(x) ^((3-x)+)(aq)+SiO₂(s)+H⁺(aq)  (5)

This reaction is reported to occur slowly at temperatures below 50° C.,but rapidly at higher temperatures. When dissolving Kaolinite clay(Al₂Si₂O₅[OH]₄), laboratory tests found no difference in the amount ofdissolved material when comparing a standard mud acid to an inhibitedmud acid made with an acid composition comprising HCl:MEA in a ratio of11.3:1, demonstrating that this preferred composition according to thepresent invention is as effective as current systems while providingstorage, environmental and handling advantages.

The aluminum fluoride produced in equation 5 (also equation 3) can alsoprecipitate above pH 2.5-3 if there is a high F/Al ratio, but thesolubility of AlF₃ is relatively high at 56 g/L.

Tertiary precipitation products are those that occur as a result of areaction of the aluminum fluorides produced in equations 3 and 5continuing to react with clays to produce a silica gel precipitate asshown in equation 6 (unbalanced):yAlF_(x) ^((3-x)+)(aq)+(x-y)Al—Si(s)+H⁺(aq)→xAlF_(x)^((3-x)+)(aq)+(x-y)SiO₂(s)  (6)

This tertiary reaction only occurs slowly at temperatures below 95° C.,and is understood to produces essentially the same precipitates as thesecondary reaction products in equation 5. Similar results to thoseobtained are expected, providing a linear performance between a standardmud acid and an inhibited HF mud acid.

Mud Acid Ratio Limitations Using Acid Composition of HCl:MEA in Ratiosof 4.4:1; 6.3:1; and 11.3:1 and Inhibited HF

Mud acids typically contain HF at concentrations of 0.5 to 3% by mass,and HCl at 4 to 15% by mass. By using acids with an enhanced HSEprofile, such as HCl:MEA (in a ratio of 4.4:1), rather than 15% HCl, theadditional MEA inhibitor will limit the amount of free HCl available insolution. The maximum amount of free HCl that would be available for mudacids made using inhibited HF and acid compositions comprising HCl:MEAin molar ratios of 4.4:1; 6.3:1; and 11.3:1.

According to another embodiment of the present invention, a few commonhigh HCl:HF ratios, such as 12:3 and 10:2, are not possible usingHCl:MEA (in a ratio of 4.4:1) and the inhibited HF according to apreferred embodiment of the present invention; to achieve these higherstrength mud acids, HCl:MEA blends with lower HSE performance (where theHCl:MEA molar ratios are 6.3:1; and 11.3:1, for example) may berequired.

Safe hydrofluoric acid (HF) compositions, those that do dissolve verysmall amounts of silica (SiO₂), were tested using amino acids as weakbase inhibitors to determine which molecular features were important. Itwas determined that an amino acid with no free basic sites such asglycine, where the amino group is protonated by the carboxylic acid,does not inhibit HF. By contrast, lysine, where only one of the aminogroups is protonated by the carboxylic acid moiety, retains a freeweakly basic site (pKa greater than 7) and does inhibit HF when it isadded at a 1 molar equivalent (or greater) relative to HF. Weak baseshaving a pKa greater than 7 which would meet these criteria includeamino acids such as: lysine, arginine, histidine, glutamine, asparagine,tryptophan, tyrosine.

Testing of Weak Base Inhibitors

Procedure:

Weak base inhibited HF formulations (A to C) were prepared by mixing theinhibitor and HF in the concentrations listed, and adding water until aclear solution was obtained, and are shown in Table 1.

TABLE 1 Weak Base Inhibited HF Test Solutions Final Solution HFInhibitor:HF Concentration Solution Inhibitor Molar Ratio (% w/w) AGlycine 1.10:1 9.3% B Lysine 0.55:1 7.9% C Lysine 1.10:1 5.2% DMonoethanolamine 1.10:1 18.5% E None 0.00:1 49.3%

In addition, tests were done with an inhibited HF solution where theinhibitor is monoethanolamine (MEA) at 1.10 molar equivalents (solutionD), and HF with no inhibitor (solution E) as comparisons. An aliquot ofeach solution was diluted with water to create 100 g of solution at 3%HF. These solutions were heated to 75° C., and 5 grams of silica wasadded to each solution, and allowed to stir for 4 hours. The solutionswere filtered to recover the undissolved silica, which was washed withwater, dried in an oven, and then weighed to determine the amount ofsilica dissolved by each solution. The amount of silica dissolved byeach solution is shown in Table 2.

TABLE 2 Silica Dissolution Testing Inhibitor:HF Dissolved SilicaSolution Inhibitor Molar Ratio (mg) A Glycine 1.10:1 442 B Lysine 0.55:1223 C Lysine 1.10:1 21 D MEA 1.10:1 3 E None 0.00:1 245

Solution E, uninhibited HF, provides a baseline silica dissolution of245 mg. An inhibited HF mixture should dissolve significantly lessmaterial, as exhibited by methanolamine (MEA) (solution D) whichdissolved only 3 mg. The glycine-inhibited solution (A), increases theamount of dissolved silica, likely due to the slightly acidic nature ofglycine. Adding 0.55 molar equivalents of lysine (solution B) providesan insufficient inhibition of HF to render it substantially safe forhandling despite showing some inhibitory effect. Increasing to 1.1 molarequivalents shows significant inhibition (solution C).

These results show that the amino acids are in their zwitterionic forms,and that glycine's only amino group is unavailable to inhibit HF.Lysine, on the other hand, has two amino groups, thus one group isalways free to interact with HF. At 0.55 molar equivalents, there isstill free HF, so silica is dissolved, but at 1.1 molar equivalents, theHF is significantly inhibited.

Based on these observations, it can be concluded that amino acids withmore than one basic site can act as HF inhibitors, as well as other weakamine bases, having a pKa greater than 7.

According to a preferred embodiment of the present invention, thecomposition can be used in oil refining (as an acid catalyst in astandard oil refinery process). According to another preferredembodiment of the present invention, the composition can be used in theproduction of organofluorine compounds including: Teflon®,fluorocarbons, fluoropolymers and refrigerants like freon. According toyet another preferred embodiment of the present invention, thecomposition can be used in the production of fluoride compounds such ascryolite, aluminium trifluoride, to name but a few examples. Accordingto another preferred embodiment of the present invention, thecomposition can be used as a pickling and cleaning agent inmetalworking. It has a great ability to remove oxides and otherimpurities from carbon steels and stainless steel. According to yetanother preferred embodiment of the present invention, the compositioncan be used, upon dilution and/or activation, as a household orindustrial rust stain remover or aluminum or other appropriate metalbrightener. According to yet another preferred embodiment of the presentinvention, the composition can be used, upon activation by another acid,for glass etching.

In the oil and gas industry, according to a preferred embodiment of thepresent invention, the inhibited hydrofluoric acid aqueous composition,said composition comprising:

-   -   hydrofluoric acid in solution; and    -   an amino acid; and        can be mixed with an acid to initiate activation, this can be        done in-situ or closed-loop—down-hole in most cases, thus        eliminating the risk of human or environmental exposure, thus        minimizing or virtually eliminating the risk of exposure to the        activated material, greatly improving safety and handling of the        material compared to the current unmodified systems utilized in        industry, which have proven fatal in the past to workers.        Preferably, the addition of the inhibited or modified        hydrofluoric acid aqueous composition is done directly into the        wellbore or closed-looped system in the case of non-oil & gas        industrial applications and, more preferably, said composition        is essentially aspirated into the system through a venturi        effect by the acid composition being injected whose purpose is        to activate the inhibited hydrofluoric acid aqueous composition.

While the foregoing invention has been described in some detail forpurposes of clarity and understanding, it will be appreciated by thoseskilled in the relevant arts, once they have been made familiar withthis disclosure that various changes in form and detail can be madewithout departing from the true scope of the invention in the appendedclaims.

The invention claimed is:
 1. An inhibited hydrofluoric acid aqueouscomposition, said composition comprising: hydrofluoric acid in solution;and a weak base selected from the group consisting of: lysine, arginine,histidine, glutamine, asparagine, tryptophan, and tyrosine; wherein saidweak base and hydrofluoric acid are present in a molar ratio of at least1.1:1.
 2. The composition of claim 1, wherein the weak base is lysine.3. A method of etching a glass, the method comprising: providing a glasssurface for etching; providing an inhibited hydrofluoric acid aqueouscomposition according to claim 1; combining said inhibited hydrofluoricacid aqueous composition with an acid composition sufficient todissociate an amount of HF required to etch glass; applying thecombination of inhibited hydrofluoric acid aqueous composition and acidcomposition to said glass surface for a sufficient time period to etchsaid glass surface.
 4. The method of claim 3, wherein the acidcomposition is selected from the group consisting of acids having a pKavalue of less than
 3. 5. The method of claim 4, wherein the acid havinga pKa value of less than 3 is methanesulfonic acid.
 6. The method ofclaim 4, wherein the acid having a pKa value of less than 3 is sulfamicacid.
 7. The method of claim 4, wherein the acid having a pKa value ofless than 3 is selected from the group consisting of: hydrochloric acid,nitric acid, sulfuric acid, modified acids, and organic acids.
 8. Themethod of claim 7, wherein the modified acid is selected from the groupconsisting of: MEA-HCl, urea-HCl, and lysine-HCl.
 9. A mud acidcomposition comprising: an inhibited hydrofluoric acid aqueouscomposition according to claim 1; and: an acid having a pKa value ofless than
 3. 10. The mud acid composition of claim 9, where the acidwith a pKa of less than 3 is selected from the group consisting of: HCl,MEA-HCl, urea-HCl, methanesulfonic acid, sulfuric acid, sulfamic acid,and lysine-HCl.
 11. The mud acid composition of claim 9, wherein theweak base is lysine.
 12. A method of using a mud acid to acidize asandstone formation, said method comprises the steps of: providing aninhibited hydrofluoric acid composition according to claim 1; providingan acid composition, said acid composition adapted to activate theinhibited hydrofluoric acid composition when put in contact therewith;combining the inhibited hydrofluoric acid composition with said acidcomposition to create a mud acid; and applying said mud acid to asilicate-containing formation and allowing said mud acid compositionsufficient exposure time to dissolve a pre-determined amount of silica.13. The method of claim 12, wherein the inhibited hydrofluoric acidcomposition is provided by injecting it directly into the acidcomposition.
 14. The method of claim 12, wherein the addition of theinhibited hydrofluoric acid composition is done by injecting it directlyinto the flowing acid composition by a venturi entrainment of theinhibited hydrofluoric acid by the acid composition.
 15. A method forremoving silica or silicate deposits on a metal surface, said methodcomprising the steps of: providing an inhibited hydrofluoric acidcomposition, according to claim 1; providing an acid composition, saidacid composition comprising a corrosion inhibitor package and adapted toactivate the inhibited hydrofluoric acid composition when put in contacttherewith; combining the inhibited hydrofluoric acid composition withsaid acid composition to create a mud acid; and applying said mud acidto the metal surface.
 16. The method of claim 15, wherein the corrosioninhibitor package comprises: a metal iodide; a terpene; a cinnamaldehydeor a derivative thereof; at least one amphoteric surfactant; a solvent;and optionally, a non-emulsifier.
 17. The method of claim 16, whereinthe metal iodide is potassium iodide.
 18. The method of claim 15,wherein the corrosion inhibitor package comprises: a metal iodide; aterpene; a cinnamaldehyde or derivative thereof; at least one amphotericsurfactant; a solvent; and a non-emulsifier.